Specific Aims: The principal objective of this study is to validate a new measure of patient outcome. The proposed instrument is a scale of cognitive functional status which is readily applicable to clinical practice and research in the elderly. This study will test the reproducibility, validity, and responsiveness of the cognitive function scale. A second objective is to integrate the results of cognitive function evaluation with those obtained using the Medical Outcomes Study instrument, which was designed to assess multiple aspects of functional status and well being, but does not include a measure of cognitive status. Integration of the cognitive function scale with the Medical Outcomes Study instrument (SF-36) will allow sensitive assessment of the negative and positive effects of medical interventions or conditions on elderly patients' mental and overall functioning in their daily lives. Experimental design and methods: This longitudinal prospective study will enroll 300 patients over the age of 65 for a baseline assessment and a second assessment, using both single-state and transition measures after six months. The patient population will consist of three groups: 100 medical clinical patients with a low comorbidity index, 100 medical clinic patients with a moderate to high comorbidity index, and 100 patients pre- and post-coronary artery bypass surgery. At both interviews, patients will complete the Cognitive Function Scale, a directed psychometric battery, the Medical Outcomes Study 36 item scale, the Geriatric Depression Scale, and the Comorbidity Questionnaire. The methodology of scale development requires that the proposed cognitive function scale satisfy the criteria of reproducibility, internal consistency, item convergent validity, variance, item discriminant validity, and construct validity. In addition, the responsiveness of the cognitive function scale will be measured by comparison with change on psychometric testing and change reported by an independent patient observer. Medical patients with low comorbidity indices are expected to show less change in cognitive functional status than medical patients with high comorbidity indices, who in turn are expected to show less change in cognitive functional status than the group of cardiac surgery patients. The interrelationship between patient- reported change in cognitive function and change in other aspects of health status, including physical, affective, social and role function and overall perception of health, will also be assessed. Long term objective: The development of a brief, easily administered, responsive, multi-item scale of cognitive function which can be used in practice and research to evaluate change in cognitive function in the elderly, and which can be integrated with other patient-centered measurements of functional status and well-being.